Regardless of what the origins of Richard II are or which works Shakespeare was inspired by, I don't believe that Richard II can be compared to anything else. Shakespeare was a very unique writer when it came to the use of language. None of his contemporaries could write like him. For example, he uses a lot of metaphors and similies in his works. And Richard II is completely written in verse, meaning that most of the couplets rhyme. And the language varies a little bit among the different characters expressing the differences in their personalities.
There might have been many literary works done on Richard II before Shakespeare's play, but none of them can compare to it in terms of eloquence.